Toshiba Corp. reached a formal agreement Monday with British Nuclear Fuels PLC to acquire the British firm's U.S. nuclear power plant arm, Westinghouse Electric Co., Toshiba officials said.

The deal, valued at some $5 billion, will be signed in London later in the day, enabling Toshiba to acquire a majority stake in Westinghouse, according to the officials.

Other companies, including trading houses Mitsui & Co. and Marubeni Corp., are expected to contribute capital to the deal, which needs to go through required procedures, including approval by the U.S. government, for formalization.

Toshiba won the bid to take over Westinghouse in competition with other companies, including Mitsubishi Heavy Industries Ltd. and an alliance between General Electric Co. of the United States and Hitachi Ltd.